Generation and Identification of Neutral CpFeC5H4X (X = O, CH2, CO) Complexes in the Gas Phase by Tandem Mass Spectrometry

Abstract

Tandem mass spectrometry experiments were performed to generate and identify neutral FcX (Fc = CpFeC5H4; X = O, CH2, CO) complexes having a formal 19-electron configuration. Neutralization−reionization mass spectra of FcX+ ions showed recovery signals corresponding to the formation of their neutral counterparts. FcO• and FcCH2• were also identified by means of the collision-induced (dissociative) ionization method as neutral products of the unimolecular fragmentation of molecular ions of the monosubstituted ferrocenes. Appearance energies of FcX ions and neutrals were measured. Activation energies for the [FcX−R]•+ bond cleavage were significantly higher than those in similar aromatic systems, PhXR•+. It was proposed that only a part of this energy was related to the FcX−R bond dissociation, the remainder being required for the intramolecular electron transfer from the ligand to the metal atom. The Fc+−CO bond dissociation energy in [FcCO]+ ions was substantially lower than that in the benzoyl ion. The weakness of the (neutral) Fc−CO bond was considered to be the major reason for the poor survival of FcCO• radicals in the neutralization−reionization of FcCO+ ions.